cregit-Linux how code gets into the kernel

Release 4.14 drivers/clocksource/i8253.c

// SPDX-License-Identifier: GPL-2.0
/*
 * i8253 PIT clocksource
 */
#include <linux/clockchips.h>
#include <linux/init.h>
#include <linux/io.h>
#include <linux/spinlock.h>
#include <linux/timex.h>
#include <linux/module.h>
#include <linux/i8253.h>
#include <linux/smp.h>

/*
 * Protects access to I/O ports
 *
 * 0040-0043 : timer0, i8253 / i8254
 * 0061-0061 : NMI Control Register which contains two speaker control bits.
 */

DEFINE_RAW_SPINLOCK(i8253_lock);

EXPORT_SYMBOL(i8253_lock);

#ifdef CONFIG_CLKSRC_I8253
/*
 * Since the PIT overflows every tick, its not very useful
 * to just read by itself. So use jiffies to emulate a free
 * running counter:
 */

static u64 i8253_read(struct clocksource *cs) { static int old_count; static u32 old_jifs; unsigned long flags; int count; u32 jifs; raw_spin_lock_irqsave(&i8253_lock, flags); /* * Although our caller may have the read side of jiffies_lock, * this is now a seqlock, and we are cheating in this routine * by having side effects on state that we cannot undo if * there is a collision on the seqlock and our caller has to * retry. (Namely, old_jifs and old_count.) So we must treat * jiffies as volatile despite the lock. We read jiffies * before latching the timer count to guarantee that although * the jiffies value might be older than the count (that is, * the counter may underflow between the last point where * jiffies was incremented and the point where we latch the * count), it cannot be newer. */ jifs = jiffies; outb_p(0x00, PIT_MODE); /* latch the count ASAP */ count = inb_p(PIT_CH0); /* read the latched count */ count |= inb_p(PIT_CH0) << 8; /* VIA686a test code... reset the latch if count > max + 1 */ if (count > PIT_LATCH) { outb_p(0x34, PIT_MODE); outb_p(PIT_LATCH & 0xff, PIT_CH0); outb_p(PIT_LATCH >> 8, PIT_CH0); count = PIT_LATCH - 1; } /* * It's possible for count to appear to go the wrong way for a * couple of reasons: * * 1. The timer counter underflows, but we haven't handled the * resulting interrupt and incremented jiffies yet. * 2. Hardware problem with the timer, not giving us continuous time, * the counter does small "jumps" upwards on some Pentium systems, * (see c't 95/10 page 335 for Neptun bug.) * * Previous attempts to handle these cases intelligently were * buggy, so we just do the simple thing now. */ if (count > old_count && jifs == old_jifs) count = old_count; old_count = count; old_jifs = jifs; raw_spin_unlock_irqrestore(&i8253_lock, flags); count = (PIT_LATCH - 1) - count; return (u64)(jifs * PIT_LATCH) + count; }

Contributors

PersonTokensPropCommitsCommitProp
Russell King15093.75%120.00%
Thomas Gleixner85.00%240.00%
John Stultz10.62%120.00%
Deepak Saxena10.62%120.00%
Total160100.00%5100.00%

static struct clocksource i8253_cs = { .name = "pit", .rating = 110, .read = i8253_read, .mask = CLOCKSOURCE_MASK(32), };
int __init clocksource_i8253_init(void) { return clocksource_register_hz(&i8253_cs, PIT_TICK_RATE); }

Contributors

PersonTokensPropCommitsCommitProp
Russell King17100.00%1100.00%
Total17100.00%1100.00%

#endif #ifdef CONFIG_CLKEVT_I8253
static int pit_shutdown(struct clock_event_device *evt) { if (!clockevent_state_oneshot(evt) && !clockevent_state_periodic(evt)) return 0; raw_spin_lock(&i8253_lock); outb_p(0x30, PIT_MODE); outb_p(0, PIT_CH0); outb_p(0, PIT_CH0); raw_spin_unlock(&i8253_lock); return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Viresh Kumar3250.00%150.00%
Thomas Gleixner3250.00%150.00%
Total64100.00%2100.00%


static int pit_set_oneshot(struct clock_event_device *evt) { raw_spin_lock(&i8253_lock); outb_p(0x38, PIT_MODE); raw_spin_unlock(&i8253_lock); return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Viresh Kumar2369.70%150.00%
Thomas Gleixner1030.30%150.00%
Total33100.00%2100.00%


static int pit_set_periodic(struct clock_event_device *evt) { raw_spin_lock(&i8253_lock); /* binary, mode 2, LSB/MSB, ch 0 */ outb_p(0x34, PIT_MODE); outb_p(PIT_LATCH & 0xff, PIT_CH0); /* LSB */ outb_p(PIT_LATCH >> 8, PIT_CH0); /* MSB */ raw_spin_unlock(&i8253_lock); return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Viresh Kumar3361.11%150.00%
Thomas Gleixner2138.89%150.00%
Total54100.00%2100.00%

/* * Program the next event in oneshot mode * * Delta is given in PIT ticks */
static int pit_next_event(unsigned long delta, struct clock_event_device *evt) { raw_spin_lock(&i8253_lock); outb_p(delta & 0xff , PIT_CH0); /* LSB */ outb_p(delta >> 8 , PIT_CH0); /* MSB */ raw_spin_unlock(&i8253_lock); return 0; }

Contributors

PersonTokensPropCommitsCommitProp
Thomas Gleixner50100.00%1100.00%
Total50100.00%1100.00%

/* * On UP the PIT can serve all of the possible timer functions. On SMP systems * it can be solely used for the global tick. */ struct clock_event_device i8253_clockevent = { .name = "pit", .features = CLOCK_EVT_FEAT_PERIODIC, .set_state_shutdown = pit_shutdown, .set_state_periodic = pit_set_periodic, .set_next_event = pit_next_event, }; /* * Initialize the conversion factor and the min/max deltas of the clock event * structure and register the clock event source with the framework. */
void __init clockevent_i8253_init(bool oneshot) { if (oneshot) { i8253_clockevent.features |= CLOCK_EVT_FEAT_ONESHOT; i8253_clockevent.set_state_oneshot = pit_set_oneshot; } /* * Start pit with the boot cpu mask. x86 might make it global * when it is used as broadcast device later. */ i8253_clockevent.cpumask = cpumask_of(smp_processor_id()); clockevents_config_and_register(&i8253_clockevent, PIT_TICK_RATE, 0xF, 0x7FFF); }

Contributors

PersonTokensPropCommitsCommitProp
Thomas Gleixner4284.00%150.00%
Viresh Kumar816.00%150.00%
Total50100.00%2100.00%

#endif

Overall Contributors

PersonTokensPropCommitsCommitProp
Russell King21539.81%111.11%
Thomas Gleixner19936.85%222.22%
Viresh Kumar10319.07%111.11%
Ralf Bächle203.70%222.22%
John Stultz10.19%111.11%
Deepak Saxena10.19%111.11%
Greg Kroah-Hartman10.19%111.11%
Total540100.00%9100.00%
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